Liquid crystal display device of in-plane switching mode, method of fabricating the same, and method of driving the same

ABSTRACT

An in-plane switching mode liquid crystal display device includes upper and lower substrates, first and second ferroelectric liquid crystal layers, a nematic system crystal layer, and first and second electrodes. The electrodes and liquid crystal layers are located between the substrates, with the nematic liquid crystal layer between the ferroelectric liquid crystal layers. The ferroelectric liquid crystal layers have different spontaneous polarization directions. An electric field is applied to the liquid crystal layers using the electrodes. The ferroelectric liquid crystal layers react to different electric field to conduct an in-plane driving of liquid crystal molecules in the nematic liquid crystal layer.

PRIORITY CLAIM

This application claims priority to patent application Ser. No.11/091,199, which claims the benefit of Korean Patent Application No.P2004-21127 filed in Korea on Mar. 29, 2004, and Korean PatentApplication No. P2004-21985 filed in Korea on Mar. 31, 2004, which arehereby incorporated by reference.

TECHNICAL FIELD

The present application relates to a liquid crystal display device ofin-plane switching mode, a method of fabricating the same, and a methodof driving the same, and more particularly, to a liquid crystal displaydevice of in-plane switching mode, a method of fabricating the same, anda method of driving the same that is possible to improve an apertureratio and to reduce a light leakage without a compensation film.

DESCRIPTION OF THE RELATED ART

A related art liquid crystal display (LCD) device controls an electricfield applied to a liquid crystal cell and modulates light incident tothe liquid crystal cell to thereby display a picture. A liquid crystalmaterial injected into the liquid crystal display device is in between asolid and a liquid, having both fluidity and elasticity.

Presently, most frequently used the liquid crystal mode of the liquidcrystal display device is a twisted nematic (TN) mode, driven by avertical electric field scheme. The TN mode has a relatively highaperture ratio. However, implementation of a wide viewing angle isdifficult because the refractive index of the liquid crystal material,which an observer senses in accordance with the viewing angle, issubstantially difficult. In addition, the response speed of the liquidcrystal material is slow.

An in-plane switching (IPS) mode is representative of a horizontalelectric field scheme. In the IPS mode, an electric field is formedbetween electrodes formed on a substrate, and liquid crystal moleculesare driven by the electric field.

FIG. 1 is a sectional view illustrating a related art liquid crystalpanel of in-plane switching mode.

Referring to FIG. 1, the related art in-plane switching mode liquidcrystal display panel includes upper and lower substrates 12 and 18,which are combined by a sealant (not shown), and upper and lowerpolarizing plates 11 and 19, which are respectively located at a rearsurface of the upper and lower substrates 12 and 18.

On the upper substrate 12, a color filter and a black matrix, etc., areformed. On the lower substrate, a pixel electrode 16 is formed inparallel to a common electrode 15, and an electric field 20 of thehorizontal direction is formed by a difference of voltages applied inbetween the electrodes 15 and 16. Liquid crystal molecules 14 arerotated within a surface direction of the substrate by the electricfield 20 to modulate a polarization component of light transmitting aliquid crystal layer.

As shown in FIGS. 2A and 2B, light transmitting axes of the upper/lowerpolarizing plates 11 and 19 are crossed vertically each other. In otherwords, if the light transmitted through the liquid crystal layer ischanged into linearly polarized light, then the light passes through theupper polarizing plate 11 to progress toward an observer. On the otherhand, if the polarization component of the light does not change whenthe light passes through the liquid crystal layer, then the light doesnot pass through the upper polarizing plate 11.

The upper polarizing plate 11 has a structure which first and secondprotective layers 11 a and 11 c are stacked with a polarizer 11 btherebetween. The lower polarizing plate 19 has a structure which firstand second protective layers 19 a and 19 c are stacked with a polarizer19 b therebetween.

The polarizers 11 b and 19 b are formed by stretching a poly vinylalcohol film and soaking it in an iodine and a dichroic dye solution toarrange iodine molecules, in parallel, in a stretching direction.

The first and the second protective layers 11 a, 11 c, 19 a and 19 c aremade of tri-acetyl cellulose TAC, etc. The first and the secondprotective layers 11 a, 11 c, 19 a and 19 c serve to prevent theoriented polarizers 11 b and 19 b from being shrunk and to protect thepolarizers 11 b and 19 b.

When the liquid crystal panel shown in FIG. 1 implements black, lightthat has been linearly polarized by the lower polarizing plate 19 is notabsorbed sufficiently by the upper polarizing plate 11, so that theamount and color of the light seen from a location out of a frontsurface of the liquid crystal display device, i.e., from a lateralsurface may be differentiated as compared with the amount and color oflight seen from the front surface of the liquid crystal display device.More particularly, as shown in FIGS. 3 and 4, when a viewing angle is±70°, light transmittance is high. Accordingly, most of the lightleakage occurs in these regions. This is because the first and thesecond protective layers 11 a and 11 c of the upper polarizing plate 11are uni-axial and have a regular delay value to change a polarizingdirection of the upper polarizing plate 11.

In order to reduce light leakage, as shown in FIG. 5, compensation films7 and 9 such as A-plate, positive C-plate, biaxial film and the like areattached to the rear surface of each of the upper and lower substrates12 and 18 together with the polarizing plate. Light leakage can bereduced by use of the compensation films 7 and 9, as shown in FIGS. 3and 6.

However, the liquid crystal panel shown in FIG. 5 has a problem thatcost increases due to the additional compensation films 7 and 9.Further, the stretching intensity is not applied uniformly over theentire area of the compensation films 7 and 9 upon stretching of thecompensation films 7 and 9 applied for a large-dimension substrate.

Moreover, in the related art IPS mode liquid crystal display, since theelectric field applied to the liquid crystal molecules 14 is bent on thepixel electrode 16 and the common electrode 15, switching of the lightis not normally performed on the electrodes 15 and 16. As a result, theIPS mode liquid crystal display has a low aperture ratio.

SUMMARY

An in-plane switching mode liquid crystal display device, a method offabricating the same, and a method of driving the same are provided withimproved aperture ratio and reduced light leakage without a compensationfilm.

In one embodiment, the in-plane switching mode liquid crystal displaydevice includes opposing substrates, opposing electrodes formed on thesubstrates, and a multilayer liquid crystal layer disposed between theelectrodes. The multilayer liquid crystal layer contains opposing layershaving a first type of liquid crystal molecules and a middle layertherebetween having a second type of liquid crystal molecules.

In another embodiment, a method of driving the liquid crystal displaydevice includes applying an electric field to the opposing layers usingthe opposing electrodes and in-plane driving liquid crystal molecules inthe middle layer by permitting one of the opposing layers to react tothe electric field.

In another embodiment, a method of fabricating an in-plane switchingmode liquid crystal display device includes forming an electrode and afirst liquid crystal layer on each of an upper and lower substrate,exposing each first liquid crystal layer to an amphiphilic oramphiphobic medium, stabilizing each of the exposed first liquid crystallayers in a mono-stable state and providing a second liquid crystallayer between the stabilized first liquid crystal layers.

In any of the above embodiments, one or more of the following may betrue: the opposing layers comprise ferroelectric liquid crystalmolecules, the ferroelectric liquid crystal molecules comprise chiralsmectic C phase liquid crystal molecules, the middle layer comprisesnematic liquid crystal molecules, the opposing layers have differentspontaneous polarization directions, liquid crystal molecules in theopposing layers react to electric fields formed by the opposingelectrodes to produce in-plane driving of liquid crystal molecules inthe middle layer, a phase difference value of each of the opposinglayers is 10 nm to 150 nm, opposing alignment films are formed on thesubstrates, each of the opposing alignment films includes an amphiphilicmedium or an amphiphobic medium, spontaneous polarization of eachopposing layer is directed toward the alignment film most proximate ormost distal to the opposing layer, only one of the opposing layersreacts to an applied electric field, the opposing layers react toelectric fields of different polarities, the opposing layers are drivenunder half V-switching mode, a phase transition of each first liquidcrystal layer causes the stabilization, each first liquid crystal layerundergoes multiple phase transitions before the second crystal layer isprovided between the first liquid crystal layers, the stabilizationoccurs without an external electric field being applied to either of thefirst liquid crystal layers, a mixture of liquid crystal material and anorganic solvent is applied to each substrate and the substrate is heatedto a temperature sufficient to vaporize the organic solvent, and/or theliquid crystal material is cooled after the organic solvent is vaporizedto produce a phase transition in the liquid crystal material (from anisotropic phase to a chiral smectic C phase possibly with a chiralnematic phase therebetween).

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description of the embodiments of the presentinvention reference the accompanying drawings, in which:

FIG. 1 is a schematically sectional view illustrating a related artliquid crystal panel of in-plane switching mode;

FIGS. 2A and 2B are plan views illustrating upper/lower polarizingplates shown in FIG. 1;

FIG. 3 is a graph showing a viewing angle property before using arelated art compensation film, and after using the related artcompensation film;

FIG. 4 is a configuration showing a viewing angle property of the liquidcrystal display panel shown in FIG. 1;

FIG. 5 is a sectional view illustrating the related art liquid crystaldisplay panel having a compensation film;

FIG. 6 is a configuration showing a viewing angle property of the liquidcrystal display panel shown in FIG. 5;

FIG. 7 is a block diagram showing an in-plane switching mode liquidcrystal display device according to one embodiment of the presentinvention;

FIG. 8 is a sectional view illustrating the in-plane switching modeliquid crystal display panel shown in FIG. 7;

FIG. 9 is a sectional view illustrating another type liquid crystaldisplay panel different from the in-plane switching mode liquid crystaldisplay panel shown in FIG. 8;

FIG. 10 is a configuration for explaining the phase difference value ofa ferroelectric liquid crystal layer shown in FIGS. 7 and 8;

FIGS. 11A to 11D are sectional views sequentially illustrating a methodof fabricating the in-plane switching mode liquid crystal display panelshown in FIG. 9;

FIG. 12 is a configuration showing a ferroelectric liquid crystalmaterial stabilized in a mono-stable state during a phase transitionprocess of FIGS. 11A to 11D;

FIGS. 13A to 13D are sectional views sequentially illustrating a methodof fabricating the in-plane switching mode liquid crystal display panelshown in FIG. 8;

FIG. 14 is a configuration showing a ferroelectric liquid crystalmaterial stabilized in a mono-stable state during a phase transitionprocess of FIGS. 13A to 13D;

FIGS. 15A and 15B are detailed configurations showing a movement ofin-plane switching mode of the ferroelectric liquid crystal material andthe nematic system liquid crystal material shown in FIG. 9;

FIG. 16 is a configuration showing a liquid crystal panel, to which aferroelectric liquid crystal layer of half V-switching mode is injected,driven by a dot inversion system;

FIG. 17 is a configuration showing a liquid crystal panel, in which anematic system liquid crystal layer is put in between the ferroelectricliquid crystal layers of half V-switching mode as shown in FIG. 8 orFIG. 9, driven by a dot inversion system;

FIGS. 18A and 18B are graphs showing light transmittance of the liquidcrystal panels shown in FIGS. 16 and 17, wherein the liquid crystalpanels are driven by the dot inversion system, respectively;

FIGS. 19A and 19B are configurations showing a viewing angle of ageneral twisted nematic mode liquid crystal display panel and thein-plane switching mode liquid crystal display panel according to oneembodiment of the present invention, respectively;

FIGS. 20A and 20B are graphs showing gray level inversion of the generaltwisted nematic mode liquid crystal display panel; and

FIG. 21 is a graph showing color coordinates in the in-plane switchingmode liquid crystal display device according to one embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings.

Hereinafter, the preferred embodiments of the present invention will bedescribed in detail with reference to FIGS. 7 to 21.

FIG. 7 is a block diagram showing an in-plane switching mode liquidcrystal display device according to one embodiment of the presentinvention.

Referring to FIG. 7, the in-plane switching mode liquid crystal displaydevice according to one embodiment of the present invention includes: aliquid crystal display panel 64 in which a nematic liquid crystalmaterial is disposed between ferroelectric liquid crystal layers; a datadriver 62 for driving a data line D of the liquid crystal display panel64; a gate driver 63 for driving a gate line G of the liquid crystaldisplay panel 64; a timing controller 61 for controlling the data driver62 and the gate driver 63; and a common voltage generator 65 forapplying a common voltage Vcom to a common electrode of the liquidcrystal display panel 64.

The timing controller 61 supplies a pixel data signal R,G,B data appliedfrom an exterior to the data driver 62. Further, the timing controller61 generates a gate control signal GDC and a data control signal DDC inresponse to control signals H (horizontal period), V (vertical period),DE, and CLK (system clock) supplied from the exterior. Herein, the gatecontrol signal GDC is for controlling the gate driver 63 and the datacontrol signal DDC is for controlling the data driver 62.

The gate control signal GDC includes a gate start pulse GSP, a gateshift clock pulse GSC, a gate output enable signal GOE, and etc. Thedata control signal DDC includes a source start pulse SSP, a sourceshift clock signal SSC, a source output enable signal SOE, a polaritycontrol signal POL, and etc.

The gate driver 63 sequentially applies a high gate voltage VGH to thegate lines GL1 to GLm in response to the gate control signal GDC fromthe timing controller 61. Accordingly, the gate driver 63 allows a thinfilm transistor TFT connected to the gate lines G1 to Gm to be driven bya gate line GL unit.

The data driver 62 applies pixel signals for each one horizontal line tothe data lines DL1 to DLn every horizontal period (H1, H2, . . . ) inresponse to the data signal DDC from the timing controller 61. Moreparticularly, the data driver 62 converts digital pixel data R, G, and Bfrom the timing controller 61 into analog pixel signals using a gammavoltage from a gamma voltage generator (not shown) to output them.

As shown in FIG. 8 or FIG. 9, the liquid crystal display panel 64includes: an upper plate 100 and a lower plate 110, which are combinedby a sealant (not shown); first and second ferroelectric liquid crystallayers 24 and 34 formed on the upper plate 100 and the lower substrate110, respectively; and a nematic liquid crystal material 50 between thefirst and the second ferroelectric liquid crystal layers 24 and 34.

The upper plate 100 includes: an upper substrate 21; a color filter (notshown) for representing a color; a black matrix (not shown) forpreventing light leakage; a common electrode 22 to which the commonvoltage Vcom generated from the common voltage generator 65 is applied;and an upper alignment film 23 applied to the common electrode 22 thataligns the first layer of ferroelectric liquid crystal molecules 24.

The lower substrate 110 includes: data lines (D1-Dn) to which datasignals are supplied; gate lines (G1-Gm) to which gate signals aresupplied; a thin film transistor (TFT) for switching liquid crystalcells at a crossing of the data lines and the gate lines; a pixelelectrode 32 connected to the thin film transistor TFT to drive theliquid crystal cells; and a lower alignment film 33 applied to the pixelelectrode 32 that aligns the second layer of ferroelectric liquidcrystal molecules 34.

Polarizers (not shown) whose light transmitting axes are verticallycrossed with each other are attached on a light incident surface of thelower substrate 110 and on a light exit surface of the upper substrate100, respectively.

The first and the second ferroelectric liquid crystal layers 24 and 34are driven in a half V-switching mode and their spontaneous polarizationdirections are different from each other.

For instance, as shown in FIG. 8, when the first ferroelectric liquidcrystal layer 24 has the same spontaneous polarization direction as anegative polarity electric field direction, the second ferroelectricliquid crystal layer 34 has the same spontaneous polarization directionas a positive polarity electric field direction. At this time, the firstferroelectric liquid crystal layer 24 reacts to the positive polarityelectric field, so that as the spontaneous polarization direction of thefirst ferroelectric liquid crystal material 24 is changed to the samedirection as the positive polarity electric field direction, the firstferroelectric liquid crystal layer 24 is driven under in-planeswitching. On the other hand, the second ferroelectric liquid crystallayer 34 reacts to the negative polarity electric field, so that as thespontaneous polarization direction of the second ferroelectric liquidcrystal material 34 is changed to the same direction as the negativepolarity electric field direction, the second ferroelectric liquidcrystal layer 34 is driven under in-plane switching.

Otherwise, as shown in FIG. 9, when the first ferroelectric liquidcrystal layer 24 has the same spontaneous polarization direction as thepositive polarity electric field direction, the second ferroelectricliquid crystal layer 34 has the same spontaneous polarization directionas the negative polarity electric field direction. At this time, thefirst ferroelectric liquid crystal layer 24 reacts to the negativepolarity electric field, so that as the spontaneous polarizationdirection of the first ferroelectric liquid crystal material 24 ischanged to the same direction as the negative polarity electric fielddirection, the first ferroelectric liquid crystal layer 24 is drivenunder in-plane switching. On the other hand, the second ferroelectricliquid crystal layer 34 reacts to the positive polarity electric field,so that as the spontaneous polarization direction of the secondferroelectric liquid crystal material 34 is changed to the samedirection as the positive polarity electric field direction, the secondferroelectric liquid crystal layer 34 is driven under in-planeswitching.

Meanwhile, as shown in FIG. 10, the first and the second ferroelectricliquid crystal layers 24 and 34 are formed to have a phase differencevalue identical to that of the related art compensation film. Forinstance, a phase difference value Δnd of each of the first and thesecond ferroelectric liquid crystal layers 24 and 34 is about 10 nm to150 nm. Herein, Δn represents a refractive index anisotropy of each ofthe first and the second ferroelectric liquid crystal molecules, and drepresents a thickness of each of the first and the second ferroelectricliquid crystal layers 24 and 34.

The nematic liquid crystal layer 50 has a switching angle of 90° andforms an interface with the first and the second ferroelectric liquidcrystal layers 24 and 34. The nematic liquid crystal layer 50 is drivenunder in plane switching by the first or the second ferroelectric liquidcrystal layers 24 and 34 as the spontaneous polarization direction ofthe nematic liquid crystal layer 50 is changed to the same direction asthe electric field direction.

FIGS. 11A to 11D are sectional views sequentially illustrating a methodof fabricating the in-plane switching mode liquid crystal display panel.Herein, the upper plate and the lower plate in FIG. 8 are manufacturedby the method as in FIGS. 11A to 11D.

An electrode 52 and an amphiphilic alignment film 53 are formed on asubstrate 51 as shown in FIG. 11A. The electrode 52 is made of atransparent conductive material such as an indium-tin-oxide (ITO). Sincethe amphiphilic alignment film 53 has electric negativity such as apolyamic acid, the amphiphilic alignment film 53 electrically representsa polarity and is made of an organic alignment material capable ofaligning a liquid crystal material. The amphiphilic alignment film 53 isrubbed in order to settle an alignment direction of ferroelectric liquidcrystal molecules.

Subsequently, a mixture in which the ferroelectric liquid crystalmaterial and an organic solvent are uniformly mixed is applied to thesubstrate 51 such that the substrate 51 is exposed to an amphiphobicmedium almost not representing electric polarity, and then the substrate51 temperature is increased to between 140° C. to 160° C. to vaporizethe organic solvent. As a result, a ferroelectric liquid crystal layer54 of an isotropic phase is formed on the substrate 51. Herein, theamphiphobic medium may be selected from an atmosphere of air or nitrogenN₂, for example.

Next, the temperature of the substrate 51 is lowered to between 110° C.to 85° C. to permit a phase transition of the ferroelectric liquidcrystal layer 54 from the isotropic phase to a chiral nematic phase (N*)as shown in FIG. 11C. Further, in order to permit a phase transitionbetween the ferroelectric liquid crystal layer 54 from the chiralnematic phase (N*) to a chiral smectic C phase (Sm C*) as shown in FIG.11D, the temperature of the glass substrate 51 is further lowered tobetween 80° C. to 50° C. At this time, as shown in FIG. 12, aspontaneous polarization Ps is generated in the liquid crystal moleculesof the ferroelectric liquid crystal layer 54 during the phase transitionto the chiral smectic C phase (Sm C*), and the direction of thespontaneous polarization Ps is directed to the amphiphilic alignmentfilm 53. In other words, while the liquid crystal molecules of theferroelectric liquid crystal layer 54 are subject to the phasetransition to the chiral smectic C phase (Sm C*), the direction of thespontaneous polarization Ps is uniformly arranged to a mono-stable statewithout an external electric field being applied.

FIGS. 13A to 13D are sectional views sequentially illustrating a methodof fabricating an in-plane switching mode liquid crystal display panelaccording to another embodiment of the present invention. Herein, theupper plate and the lower plate in FIG. 9 are manufactured by the methodas in FIGS. 13A to 13D.

An electrode 52 and an alignment film 53 are formed on a substrate 51 asshown in FIG. 13A. The electrode 52 is made of a transparent conductivematerial such as an indium-tin-oxide (ITO). The alignment film 53 ismade of an organic alignment material such as a polyamic acid, and thealignment film 53 is rubbed in order to settle an alignment direction offerroelectric liquid crystal molecules.

Subsequently, a mixture in which the ferroelectric liquid crystalmaterial and an organic solvent are uniformly mixed is applied to thesubstrate 51, which is exposed under an amphiphobic medium, e.g., underan atmosphere of H₂O or O₂, having a high electric negativity (i.e., ahigh polarity) compared to the alignment film 53 as shown in FIG. 13B,and a temperature of the substrate 51 is increased to between 140° C. to160° C. to vaporize the organic solvent. As a result, a ferroelectricliquid crystal layer 54 of an isotropic phase is formed on the substrate51.

In order to produce a phase transition in the ferroelectric liquidcrystal layer 54 from the isotropic phase to the chiral nematic phase(N*) as shown in FIG. 13C, the temperature of the substrate 51 islowered to between 110° C. to 85° C. Further, in order to produce aphase transition in the ferroelectric liquid crystal layer 54 from thechiral nematic phase (N*) as shown in FIG. 13C to the chiral smectic Cphase (Sm C*) as shown in FIG. 13D, the temperature of the substrate 51is further lowered to between 80° C. to 50° C. At this time, as shown inFIG. 14, a spontaneous polarization Ps is generated in the liquidcrystal molecules of the ferroelectric liquid crystal layer 54 duringthe phase transition process transited to the chiral smectic C phase (SmC*), and the direction of the spontaneous polarization Ps is directedtoward the amphiphilic medium on the opposite side to the alignment film53. This is because the amphiphilic medium on opposite the alignmentfilm 53 has a higher electrical negativity than the alignment film 53.In other words, while the liquid crystal molecules of the ferroelectricliquid crystal layer 54 are subject to the phase transition to thechiral smectic C phase (Sm C*), the direction of the spontaneouspolarization Ps is uniformly arranged to a mono-stable state without anexternal electric field being applied.

FIGS. 15A and 15B are sectional views illustrating a method of drivingthe liquid crystal display device according to one embodiment of thepresent invention. For instance, FIGS. 15A and 15B represent a change ofthe ferroelectric liquid crystal molecules arrangement of the halfV-switching mode when respective external electric fields (E(+)) and(E(−)) of a positive polarity and a negative polarity are applied to thehalf V-switching mode ferroelectric liquid crystal molecule arrangementaligned in a direction corresponding to the negative polarity electricfield (E(−)).

As shown in FIG. 15A, when a positive polarity electric field is appliedto the liquid crystal display panel having the first and the secondferroelectric liquid crystal materials 24 and 34 and the nematic liquidcrystal material, the spontaneous polarization direction of the firstferroelectric liquid crystal material 24 is changed to the samedirection as the positive polarity electric field direction. The firstferroelectric liquid crystal material 24 is then driven in the in-planedirection and the nematic liquid crystal material adjacent to the firstferroelectric liquid crystal material 24 is driven under the in-planeswitching. The second ferroelectric liquid crystal material 34 havingthe same spontaneous polarization direction as the positive polarityelectric field direction does not react to the electric field andmaintains an incipient arrangement state. At this time, as the nematicliquid crystal material 50 is switched in plane only by the firstferroelectric liquid crystal material 24, the nematic liquid crystal 50becomes twisted in a vertical direction.

Furthermore, as shown in FIG. 15B, when a negative polarity electricfield is applied to the liquid crystal display panel having the firstand the second ferroelectric liquid crystal materials 24 and 34 and thenematic liquid crystal material, the spontaneous polarization directionof the second ferroelectric liquid crystal material 34 is changed to thesame direction as the negative polarity electric field direction. Thesecond ferroelectric liquid crystal material 34 is then driven in thein-plane direction and the nematic liquid crystal material adjacent tothe second ferroelectric liquid crystal material 50 is driven under inplane switching. Further, the first ferroelectric liquid crystalmaterial 24 having the same spontaneous polarization direction as thenegative polarity electric field direction does not react to theelectric field and maintains an incipient arrangement state. At thistime, as the nematic liquid crystal material 50 is switched in planeonly by the second ferroelectric liquid crystal material 34, the nematicliquid crystal 50 becomes twisted in a vertical direction.

The in-plane switching mode liquid crystal display device assuresimplementation of a wide viewing angle by virtue of in-plane driving ofthe nematic liquid crystal 50 as well as minimizing deterioration of theaperture ratio by applying an electric field to the liquid crystal 50under a vertical electric field scheme. Further, since the nematicliquid crystal 50 is rapidly moved by the ferroelectric liquid crystalmaterials 24 and 34, it is possible to improve the response speed of thenematic liquid crystal 50.

FIG. 16 is a configuration showing a liquid crystal panel to which ahalf V-switching mode ferroelectric liquid crystal layer is driven bydot inversion, and FIG. 17 is a configuration showing a liquid crystalpanel, in which a nematic liquid crystal layer between the halfV-switching mode ferroelectric liquid crystal layers as shown in FIG. 8or FIG. 9, is driven by dot inversion.

As shown in FIG. 16, if a liquid crystal display device having a halfV-switching mode ferroelectric liquid crystal cell aligned by a negativepolarity electric field is driven by dot inversion, then theferroelectric liquid crystal cells transmit light alternately one by onebecause the ferroelectric liquid crystal cell transmits light only inthe positive polarity electric field. In other words, the odd liquidcrystal cells of an odd horizontal line and the even ferroelectricliquid crystal cells of an even horizontal line transmit light inresponse to the positive polarity electric field (+) in an odd frame andintercept light in response to the negative polarity electric field (−)in an even frame. Even liquid crystal cells of an odd horizontal lineand odd ferroelectric liquid crystal cells of an even horizontal lineintercept light in response to the negative polarity electric field (−)in an odd frame and transmit light in response to the positive polarityelectric field (+) in an even frame. At this time, as shown in FIG. 18A,60 Hz data, i.e., the electric field of which polarity is inverted ateach frame period, is applied to a free liquid crystal cell. The liquidcrystal cell transmits light only in an odd frame period (1 Fr, 3 Fr, 5Fr) to which the positive polarity electric field is applied.Accordingly, if the half V-switching mode ferroelectric liquid crystalcell is uniformly aligned under electric field through the whole paneland is driven in an inversion system, then because a visitor perceiveslight periodically at each frame period, the brightness of displaypicture is lowered and the display picture flickers.

On the other hand, as shown in FIG. 17, if the half V-switching modeliquid crystal display panel in which the nematic liquid crystal layeris between the first and the second ferroelectric liquid crystal layersis driven by dot inversion, then one of the first or the secondferroelectric liquid crystal layers is in-plane switched in the positivepolarity electric field and the another is in-plane switched in thenegative polarity electric field. For instance, the first ferroelectricliquid crystal layer is in-plane switched in the positive polarityelectric field and the second ferroelectric liquid crystal layer isin-plane switched in the negative polarity electric field.

In other words, the odd liquid crystal cells of an odd horizontal lineand the even ferroelectric liquid crystal cells of an even horizontalline transmit light in response to the positive polarity electric field(+) in an odd frame and transmit light in response to the negativepolarity electric field (−) in an even frame. Even liquid crystal cellsof an odd horizontal line and odd ferroelectric liquid crystal cells ofan even horizontal line transmit light in response to the negativepolarity electric field (−) in an odd frame and transmit light inresponse to the positive polarity electric field (+) in an even frame.At this time, as shown in FIG. 18B, 60 Hz data, i.e., the electric fieldof which polarity is inverted in each frame period, is applied to a freeliquid crystal cell. The liquid crystal cell transmits light in an oddframe period (1 Fr, 3 Fr, 5 Fr) to which the positive polarity electricfield is applied and transmits light in an even frame period (2 Fr, 4Fr, 6 Fr) to which the negative polarity electric field is applied.Accordingly, even though the half V-switching mode ferroelectric liquidcrystal cell is uniformly aligned under electric field through the wholepanel and is driven in an inversion system, because a visitor perceiveslight periodically every frame period, the brightness of display pictureis improved.

FIGS. 19A and 19B are configurations showing a viewing angle of atwisted nematic mode general liquid crystal display panel and thein-plane switching mode liquid crystal display panel according to thepresent invention, respectively. In FIGS. 19A and 19B, azimuth angles90°, 270°, 180° and 0°, respectively, represent upper/lower/left/rightviewing angles. Concentric circles represent inclination angles, whichis inclined from a display surface to the declination angle.

As shown in FIG. 19A, the general twisted nematic mode liquid crystaldisplay device can obtain contrast ratio of 100 at an inclination angle10° for azimuth angles 45°, 135°, 225°, and 315°, and can obtaincontrast ratio of 0 to 10 at inclination angles more than 50°. In otherwords, in the general twisted nematic mode liquid crystal displaydevice, the range of viewing angles capable of obtaining a high contrastratio is relatively narrow.

Further, in the general twisted nematic mode liquid crystal displaydevice brightness in accordance with the viewing angle ofupper/lower/left/right directions should be increased by an appliedvoltage. However, gray level inversion occurs, decreasing the brightnesseven through the applied voltage is increased. For instance, as shown inFIG. 20A, brightness of a “0” gray level is increased more than that ofa “95” gray level near about 50° in left/right directions. Also, asshown in FIG. 20B, brightness of a “255” gray level is decreased morethan that of a “223” gray level, and brightness of a “191” gray level isdecreased more than that of a “63” gray level, near about 20° to 30° inupper/lower directions.

As shown in FIG. 19B, the in-plane switching mode liquid crystal displaydevice according to the present invention can obtain contrast ratio of100 at an inclination angle 40° for azimuth angles 45°, 135°, 225°, and315°, and can obtain contrast ratio of 10 at an inclination angle 70°.Moreover, since the viewing angle is symmetric in theupper/lower/left/right directions, the range of upper/lower/left/rightviewing angles is wide. In other words, the present in-plane switchingmode liquid crystal display device has a relatively wider viewing angleand has a higher contrast ratio compared to the general twisted nematicmode liquid crystal display device. Furthermore, since a colorcoordinate in the in-plane switching mode liquid crystal display deviceis located adjacently with a coordinate of standard white light([x,y]=[0.329,0.333]) as shown in FIG. 21, adjustment of the whitebalance is easy.

As described above, in the in-plane switching mode liquid crystaldisplay device, the method of fabricating the same, and the method ofdriving the same, each of the first and the second ferroelectric liquidcrystal layers formed in the upper and lower substrates, respectively,reacts to the electric fields of opposite polarities, so that the liquidcrystal molecules of a nematic liquid crystal layer is driven under inplane switching. As set forth above, the first and the secondferroelectric liquid crystal layer react to the opposite polarityelectric fields, thereby permitting a picture in the entire frameirrespective of the polarity of the voltage applied thereto. Further,the nematic liquid crystal material is in-plane switched by theferroelectric liquid crystal layer and the phase difference of theferroelectric liquid crystal layer is identical to that of acompensation film. Accordingly, it is possible to prevent light leakagegenerated in the lateral surface of the polarizing plate without usingthe compensation film.

Although the present invention has been explained by the embodimentsshown in the drawings described above, it should be understood to theordinary skilled person in the art that the invention is not limited tothe embodiments, but rather that various changes or modificationsthereof are possible without departing from the spirit of the invention.Accordingly, the scope of the invention shall be determined only by theappended claims and their equivalents.

1. A method of driving a liquid crystal display device having opposingsubstrates with opposing electrodes thereon and a multilayer liquidcrystal layer disposed between the electrodes, the multilayer liquidcrystal layer containing opposing layers of a ferroelectric liquidcrystal molecules and a middle layer therebetween of a nematic liquidcrystal molecules, the method comprising: applying an electric field tothe opposing layers using the opposing electrodes; and in-plane drivingliquid crystal molecules in the middle layer by permitting one of theopposing layers to react to the electric field, wherein the opposinglayers are driven in a half V-switching mode, and their spontaneouspolarization directions are different from each other so that one of theopposing layers is react to a positive electric field and the other oneof the opposing layers is react to a negative electric field, andwherein the in-plane switching mode liquid crystal display is driven bya dot inversion in that the positive electric field and the negativeelectric field are applied to adjacent liquid crystal cells at the sametime, so that the positive electric field is applied to the multilayerliquid crystal layer of a first liquid crystal cell in an odd frame andthe negative electric field is applied to the multilayer liquid crystallayer of a second liquid crystal cell adjacent to the first liquidcrystal cell in the odd frame.
 2. The method according to claim 1,wherein the first liquid crystal cell comprises a odd liquid crystalcell of an odd horizontal line and a even liquid crystal cell of an evenhorizontal line, and the second liquid crystal cell comprises a evenliquid crystal cell of the odd horizontal line and a odd liquid crystalcell of the even horizontal line.
 3. The method according to claim 1,wherein the first liquid crystal cell transmits light in response to thepositive polarity electric field in the odd frame and transmits light inresponse to the negative polarity electric field in an even frame, andthe second liquid crystal cell transmits light in response to thenegative polarity electric field in the odd frame and transmits light inresponse to the positive polarity electric field in the even frame.